A -ray View on MWL Studies of Blazars. Stefan J. Wagner LSW Heidelberg

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1 A -ray View on MWL Studies of Blazars Stefan J. Wagner LSW Heidelberg

2 MWL studies of Blazars Marscher, ApJ 216, 244, 1977

3 MWL studies of Blazars Marscher, ApJ 216, 244,

4 rays: Top End and Bottom End log S log [Hz] Measured SED ( , a.k.a. Mrk 421) - Covering an additional 10 orders of magnitude - XBLs Synchrotron emission extends to 1020 Hz - Plotting S rather than S

5 rays: Top End and Bottom End log [Hz] Cosmic Rays (full sky average) (S. Swordy) Modified: drop at GZK cutoff

6 rays: Top End and Bottom End log dn/de [arbitrary units] Flux of Mrk 421 log [Hz]

7 High Energies - Few Photons TeV: 10 orders of magnitude higher energies compared to X-rays 20 orders of magnitude fewer photons (1) Experimental challenges (seeing anything) (2) statistical challenges (poissonian noise in unevenly sampled data) (3) methodological challenges (few photons and no photons are not very different, unless few photons get published and no photons get not) upper limits are better then nothing, but flux-data with errors of the same measurements are much more useful.

8 Complimentary Techniques Space-borne Fermi LAT 1 m2, 100%, 1.5 sr 108 s exposure all sky Week-decades, very homogeneous 100 MeV 100 GeV Ground: HESS MAGIC VERITAS 105 m2, 10%, sr high dynamic range hours - weeks 100 GeV 10 TeV Complementary time-scales and energy ranges

9 Noise processes and time scales Variability spectra described by power laws (red noise or 'reddish' noise) Suggests stochastic processes (what are physics implications?) Flare = Increased emission from a distinct volume. Causality still constrains light-crossing times (implict assumption of vanishing acceleration times) Which processes can change fastest? Acceleration radiation amplification absorption crossing In all leptonic models, -rays cover high-energy end, complementing the synchrotron range does this constrain the choices?

10 Rapid ('Intraday') variability The IDV problem: rapid variability implies a compact emission region. Iteration of the 'Quasar problem': How to get so much light out of a small volume beaming uncomfortable What happens? more light/particle, more particles, (higher energy)? Cooling/acceleration time scales depend on energy MWL studies M87, GMVA At most few variable sub-volumes Small r does not imply small d

11 Is GHz IDV intrinsic? GHz IDV is real (even if it was considered to be impossible). 1) Inferred brightness temperatures exceed IC limit. Is the limit applicable? 2) Interstellar scintillation is an unavoidable process. Does it exclusively cause IDV? (right timescales, right frequency dependence) Trace IDV across the spectrum (many times) , WW, ARAA Plot IDV radio-optical

12 Is GHz IDV intrinsic? GHz IDV is real (even if it was considered to be impossible). 1) Inferred brightness temperatures exceed IC limit. Is the limit applicable? 2) Interstellar scintillation is an unavoidable process. Does it exclusively cause IDV? (right timescales, right frequency dependence) Dave Jauncey: pattern-offset across continents, annual cycle in IDV timescales. Scintillation causes GHz IDV But: Scintillation faces the same problem (1) And: Some IDV is intrinsic (gravitational lensing)

13 Is GHz IDV intrinsic? GHz IDV is real 1) Inferred brightness temperatures exceed IC limit. Is the limit applicable? 2) Interstellar scintillation is an unavoidable process. Does it exclusively cause IDV? (right timescales, right frequency dependence) Dave Jauncey: pattern-offset across continents, annual cycle in IDV timescales. B with 10.5d offset between images A & B (15 GHz) Biggs, Brown, Wilkinson, MN 323, 995 (2001) And: Some IDV is intrinsic (gravitational lensing)

14 rays and Compton catastrophe Brightness temperature limit 1012 K. For higher TB (radiation densities) Compton losses are expected: (TB10 in 2nd order Compton scattering). Do we observe this in the gamma-ray domain? GHz emission due to electrons with ~ IC boosts photons by 2. 1st order/ 2nd order IC boosts GHz into optical / X-ray regime.

15 rays and Compton catastrophe Brightness temperature limit 1012 K set by ratio of synch/ic losses. TB10 scaling consequence of particle spectra extending to thermal limit. The high photon densities are due to lowest energy electrons. Electron spectra with min ~100 have lower photon densities/ic losses despite exhibiting similar GHz fluxes TB limit increases. Lowest energy electrons are not seen in synchrotron/ic data Several lines of arguments suggest min > 100. Effective TB limit likely to be significantly higher than 1012K in small volumes (with cooled particles diffusing to larger out) [Irrespective of strong suppression of IC catastrophes by beaming]

16 Look elsewhere Scintillation (unavoidable) is likely a significant contribution to GHz-IDV Separating it from all GHz-IDV is difficult. Can we address the problem in another way? Higher radio frequencies (37 GHz, 230 GHz) do not avoid scintillation. What is happening to low-energy end of particle distribution in compact sub-volumes during flares? X-ray IDV in sources whose 1017 Hz emission is IC dominated (low E) Cross-correlate high E end (synch, opt) and low E end (IC, X-ray)

17 Low E particles and high E photons Ferrero & SW, 2005, Ferrero et al., 2006 Low-Energy cut-off Tsang & Kirk, 2007

18 The gamma-ray view ldv by low-energy electrons exists. Can we trace IDV (particle energy) in IC instead of synchrotron? IDV in gamma-ray domain (despite the low photon fluxes)

19 Rapid -ray variability IDV in gamma-ray domain exists but it is still unclear whether we can trace IDV (particle energy) in IC: 1: Even at shorter timescales (e.g. PKS ) 2: Is the IC truly leptonic? 3: Are X-rays in SSC domain? 4: In LBLs the SEDs favor multiple processes.

20 Leptonic emission IDV in gamma-ray domain exists but it is still unclear whether we can trace IDV (particle energy) in IC: 1: Even at shorter timescales (e.g. PKS ) 2: Is the IC truly leptonic? Expect a good match to HE synchrotron 3: Are X-rays in SSC domain? 4: In LBLs the SEDs favor multiple processes

21 Leptoni emission Continuous optical monitoring of since 2008 and Fermi-LAT: P8 allows 2d binning with TS>40 for 85% of all bins Good match on long and short timescales for 70% of all bins Unique scaling for 60% of all bins (Wagner, Kurtanidze, Mohamed, in prep.)

22 Leptonic emission Continuous optical monitoring of since 2008 and Fermi-LAT: P8 allows 2d binning with TS>40 for 85% of all bins Good match on long and short timescales for 70% of all bins Unique scaling for 60% of all bins (Wagner, Kurtanidze, Mohamed, in prep.)

23 Multiple components IDV in gamma-ray domain exists but it is still unclear whether we can trace IDV (particle energy) in IC: 1: Even at shorter timescales (e.g. PKS ) 2: Is the IC truly leptonic? Expect a good match to HE synchrotron 3: Are X-rays in SSC domain? Most bright gamma-ray sources are HBLs (X-rays are synch.) 4: In some LBLs the SEDs favor multiple components Zacharias & SW, 2016

24 Multiple components Gamma ray domain displays multi-component SEDs (M. Mohamed) Suggested in many objects in SEDs Composed of data from Non-simultaneous observations (e.g. Fermi LAT and VHE data) In simultaneous data it is often difficult to cover a sufficiently wide energy range. Several options to explain hardening, but multi-particle components is often the preferred option.

25 Multiple components Different components with different variability patterns PKS (HESS coll. and Fermi coll., 2009) VHE matches better to optical synchrotron than to X-rays (opposite to LAT) Inconsistency to simple models. Flares due to changes in particle spectrum?

26 Summary Rapid variability is observed throughout the EM spectrum. Intrinic variability by low energy particles (direct and indirect) IC catastrophes are not inevitable; SSC(GHz) not in -ray range Many objects exhibit continuous optical-gamma correlations without lags and little scatter in Compton dominance However: A growing number shows clear evidence of distinct multi-component particle distribution functions Advertisement: LAT-0716 photon arrival time project: Talk to me, or lsw.uni-heidelberg.de